Hello, and welcome to the Physics World Stories
podcast. I'm Andrew Blester.
And in this episode, we're going to be
exploring
comet three I ATLAS.
High above the orbital plane of our solar
system, the comet is currently screaming past us
at 58 kilometers per second.
It started its journey, if the latest data
is correct,
thirteen billion years ago in the thick dust
of the young Milky Way is a relic
of the cosmic noon, a time capsule from
an era before our sun even existed.
It was first spotted in July 2025,
and the internet did what it does best
it speculated.
With the velocity nearly double that of the
first interstellar visitor we knew about Oumuamua
and a trajectory that seemed to defy easy
tracking from earth based telescopes
the
alien probe headlines
practically wrote themselves.
But as physicists,
we know that the natural truth is far
more profound than the science fiction. Today on
the Physics World Stories podcast, we're looking at
three I atmos through a more sensible
scientific lens, and I would argue a more
fascinating one. We're joined by doctor Tracy Becker,
a lead on the team that has used
the sensors of the Europa Clipper mission to
observe the comet
from a unique perspective.
We're also talking to Michelle Quippus from the
European Space Agency. Michelle is a key figure
in the comet interceptor mission, a daring project
designed to park a spacecraft
deep in space
and wait for a comet to arrive.
We'll hear about that mission later in the
podcast, but first to doctor Tracy Becker. I'm
a planetary scientist at the Southwest Research Institute,
which is located in San Antonio, Texas.
And, primarily, I study icy small bodies like,
Europa, which is one of the moons of
Jupiter,
and,
asteroids
and,
planetary rings. So rings around Saturn,
Uranus, Neptune. So that's really awesome, and I
feel like that's what we should be talking
to you about. But we're actually talking to
you about three I Atlas.
How have you come into this story?
So it's actually really
exciting because when,
we first heard about the interstellar object,
it was
back in July. It was, like, July 4
weekend, just before that when it was first
discovered. And I was in a meeting with
the with some of the Europa Clipper team,
and I said, wow. Wouldn't it be so
cool if we could observe it?
But that was like a throwaway sentence. I
didn't know anything about the geometry of where
the where the object was versus where Europa
Clipper was or anything like that. And then
and then it was the holiday, so everyone
kinda forgot about it. But somehow over the
weekend,
that the lead of the mission, the project
scientist, Bob Papalardo, reached out to the UVS
team, which is the instrument that I work
on, Europa UVS, and asked, you know, would
we be able to observe it? And we
were like, absolutely. They sent us,
one of the other scientists on the team
had put together a little
diagram with the geometry of where is the
spacecraft, where is the comet gonna be on
closest approach, and,
where is the sun and all of that
geometry. And when we looked at it, we're
like, this is
an incredible opportunity to observe this object with
our with our spacecraft. And so,
we were excited and got busy right away
because we only had a couple of weeks
to plan the observations
and get the commanding of the instrument onboard
the spacecraft,
in time for the observations that were gonna
happen,
in early November.
So it it so it's Europa Clipper. Right?
It's it's going tell us a bit about
what it's going to do
because I want to ask you next, how
easy is it is to essentially
turn it? I I do you have to
turn it? How do you repurpose it all?
That's a great question. So Europa Clipper was
launched in October 2024, and it's on its
way
to, the Jupiter system to study Europa, which
is this really interesting moon of Jupiter that
is mostly an ice
shell made out of water ice as we
know it here on Earth, water ice. But
underneath that icy shell is liquid
is an ocean of liquid water, and there's
more liquid water there than in all of
Earth's oceans combined
times two. And so if there's anywhere in
the solar system to look for life, or
the signs of the, habitability,
that's the place to go and check. And
so that mission is really designed with the
goal of habitability in mind. It's it's meant
to understand the conditions of
of Europa, the the geology, the interior ocean.
You know? Is the temperature? Is the salinity,
sufficient to support life as we know it?
We're not necessarily trying to say, yes. Life
is there or not. But certainly understanding
that first step of are the conditions there
even favorable
for the existence of life.
That's insanely exciting.
Yes. Very.
I know. 2001.
Right? And then 2010,
those science fiction books. Hands off, Europa. That's
ever since then,
I've wanted to get my hands on Europa,
and you're actually doing it. Yeah. That's insane.
Oh, yeah. When somebody says, you know, don't
go there. That's where we're gonna go.
And we do have a we have a
monolith at every one of our, team meetings
to, you know, commemorate where we're going. What
sorry. When's it getting there? When's it when's
it gonna arrive? Yeah. So it's it's on
a on a six year journey. And, actually,
the spacecraft will be doing a flyby of
the Earth and the moon to get a
gravity assist later this year in 2026.
And then, and then it will be
a direct shot out to the Jupiter system
and is planned to arrive in 2030.
Okay.
And then the data will get to you
when?
Well, we'll start collecting data as soon as
we get there, and, it takes just the
time
of the speed of light. So depending on
where Jupiter is compared to the distance of
Earth anywhere between a half hour and two
hours or something like that to get start
getting some of those bits down. When you
say the data, has it also got cameras
on it? Oh, yeah. There's a full suite
of instruments. This is a considered to be
a NASA flagship mission, so it's kind of
got all the things we could possibly fit
on board and still launch the spacecraft. So
it has
a really powerful camera. We're gonna get images
that are completely
mind blowing compared to the images that we
have from, for example, the Galileo spacecraft. We're
gonna get some really, really beautiful
shots. We have a magnetometer on board because
that's one of the best ways to sense,
the ocean underneath is to actually understand the
magnetic field and how how Europa's
induced magnetic field due to its ocean
deflects the magnetic field of Jupiter. So that's
actually one of the main ways we know
about that ocean. So we have a magnetometer.
We have a plasma instrument that also helps
measure those kinda interactions with magnetic field.
There's a radar, a ground penetrating radar to
try to pierce through the ice and maybe
hit where that, ocean deck starts
and,
an infrared spectrometer to understand the composition of
Europa's ice. Because while it's mostly water ice,
we see these really interesting discolorations
that we think, are generally they kind of
fall line along these lines of cracks and
and breakups of the ice that we see.
So that might indicate that that water is
coming from underneath that ocean up to the
surface and refreezing.
And so if we can understand the composition
of those discolorations,
maybe we can say something about the materials
that are in that ocean underneath.
Let's see. I don't wanna miss any oh,
and then and then the instrument that I
work on, of course, is the UV instrument,
ultraviolet studies of Europa that are mostly focused
on the atmosphere, the very thin atmosphere of
Europa. And then we have two in situ
instruments. One,
one is a dust collector, and one is
a gas sniffer, a mass spectrometer. And so
from those, we can actually
collect the dust the dust and collect the
gas and analyze them on board and send
that data back down. And that's a way
to basically taste and sniff the the composition
of whatever material might be up in the
atmosphere of Europa.
Oh, amazing. Listen.
Can we make a promise that if I'm
still making this podcast
in 2030,
you talk to me again about it then?
Absolutely.
Awesome. Let's do that. But you what you
have done is and you and your team
have turned,
Europa Clipper. Did you turn it? It's going
to do that. But while we're there, on
the way, let's look at this comet.
Yeah. So,
on this as a scientist on the scientist
side, we just kind of say, hey. We
wanna look at it. Right? And and then
the engineers have to go and figure out
how to do it.
But, yeah, the spacecraft was not necessarily meant
to be pointing that direction.
So they do have to take into a
lot of they have to take a lot
of things into account when turning the spacecraft.
Things like where are the solar panels going
to be pointing because we have these huge
solar panels on board, but you don't want
to point them away from the sun all
of a sudden and then lose power.
And so it is it's a very big
spacecraft, and it's slow. It takes a while
to slew.
But we're kinda just, you know, on this
journey out to Jupiter, and there's not much
else not too much else going on, I
would say. And so,
it was
feasible in that sense. We were in the
middle of doing a lot of our calibrations.
And so one of the things that actually
worked out was that in our for our
instrument in particular,
we weren't going to be able to understand
how,
an object other than a star
kind of
what that data would look like in our
detector. And so a star is a point
source. It's very kinda sharp, clean signal,
but we have this very narrow slit. And
so Europa, when we get there, it's gonna
be bigger than our slit size. And the
effects of that on the detector are appreciable.
And so we wouldn't be able to understand
those until we already were at Europa already
taking data.
And so this actually presented an opportunity for
what we call a calibration where we could
look at an object that had an angular
size,
that would fill the slit and,
use that as a way to start to
already get a sense of how does our
detector work when we're looking at a a
big object other than a star. And so
that kinda worked together. So we actually were
able to move around some of our other
planned calibrations
and replace it with this with this special
observation and still use it for calibration, but
also get really, really cool science.
Okay. So what have you seen by looking
at it then?
That's a good question, and we're still figuring
it out. So we we the UV instrument,
it's interesting, right, because it's designed to look
at Europa, but mostly Europa's atmosphere. And so
one of the things that it's meant to
do is understand how,
molecules
in in the gas form kind of break
up, and they they send out a signal.
When when you have a breakdown of any
kind of compound
or or,
yeah, elemental material,
it releases light at a certain wavelength. And
so, for example, if you have
o two, two oxygen molecules, and they break
up, they're gonna send out a signal at
a very, very specific wavelength, and that is
a very strong signal at at UV wavelengths.
Lengths. And so that's what we're planning to
do at Europa. It happens to work out
nicely for a comet where comets are also
constantly getting interactions with the sunlight, and that's
kind of breaking apart some of the molecules
that are making up its gas coma. And
so as those molecules break apart, they send
out these signals to us. Well, they just
send out the signals, and we can capture
those with our cameras
and understand basically what what that composition is.
So it's really a way of understanding what
the comet is made out of. And so
it works
really well as a as a comet instrument
too. And, in fact, there are UV instruments,
that are orbiting Mars and UV instruments on,
the the Lunar Reconnaissance Orbiter around the moon
that also tried to look at, at, at
three I Atlas, and I'm not sure what
all of those results are yet. But they
and then in Hubble Hubble data and Swift
data. So everything was kind of looking in
the UV. It's really actually a a a
perfect wavelength to be looking at and studying
comets.
And so what did we see so far?
So we saw
some really interesting
signatures. The the main one is that we
we definitely see lots and lots of hydrogen,
which was not unexpected by any stretch. And
we also see a lot of oxygen. Both
of those are coming from the central coma,
that gas that's kind of sublimated off of
the main comet and kinda hangs around the
comet.
That part is completely expected. We also definitely
see other signatures of materials, but we're still
trying to understand our detector because, remember, we
were still in the calibration phase where we're
understanding
exactly how the detector works and what,
the signal the signal's coming in, exactly what
wavelengths they are, and then seeing how much
of that might be carbon or might be,
sulfur or argon or whatever other materials might
be there. And so we are still in
that process of figuring it out, but we
do think we see a a bit of
carbon and,
probably a few other things.
The other main thing that we see definitely
in the data itself is sort of the
scattered light coming from
the from probably from the tail. So we
think that the the dust tail that kind
of gets,
trails off of the edge of the the
comet,
that those different dust particles are basically
scattering sunlight into our into our detector, and
we're measuring those as well.
The intriguing things that we're seeing is that
we definitely see what's known as the tail,
the ion tail, which is usually when the
gas,
sublimates when it when it comes off of
the the comet,
then it interacts with the sun. You have
this pressure from the solar wind, and that
usually makes an anti sunward
tail. We see that one. That one kinda
lines up with kind of all of the
expectations.
But we also see some tail structure going
towards the sun,
and we're not the only ones. Other people
have seen sort of this anti they call
it the anti tail even though it's the
tail that's going towards the sun.
They're seeing other other instruments are seeing that
as well, but we're still trying to figure
the way we're seeing it out. We're seeing
it from a very different perspective than most
of the other spacecrafts that have looked at
this object have seen it. They are you
know, most of the objects most of the
telescopes, the observations have come from,
from Earth based telescopes. Right? It's from Hubble
or from JWST
or from ground based telescopes.
Where we were, we're actually looking at the
night side of the comet. So we're actually
looking the comet is kind of in between
us and the sun, more or less. And
so we're getting it from a very different
angle. And and so far, what we're seeing
on that sunward facing tail and maybe that
dust tail,
is not lining up exactly with what would
be predicted. And so we're trying to figure
out, is it how we're viewing it? Is
it geometry, or is it something that we're
able to see that the other ones can't
because of that unique lighting geometry that we
have?
Okay. I mean but that doesn't mean it's
aliens. Right? No. It definitely does not mean
it's aliens.
I would expect something way more fun than
just
a just a a a tail that's in
the wrong direction if it were aliens.
I would hope it would spill out something
or make it pretty drawing or something like
that. Oh, hey. That would be cool, wouldn't
it? Like, hello.
That sort of thing. I've or maybe they
wouldn't choose English. Who knows? But, well, I
mean, it doesn't make a lot of sense,
does it, that that there'd be a tail
going that way?
Yeah. I don't know. As a not comet
person, as someone who's meant to be studying
Europa,
I think it's not completely unheard of to
see some of these sunward facing
tails, but they're yeah. And it's hard to
say how much of what we're seeing is
coming from the dust, how much of it
is coming from a gas tail that somehow
sunward facing.
I don't know. I mean, it's it's fun
to get to play with it, though, and
try to figure out this mystery.
I think that's probably the best part about
it.
So when you say what you've seen so
far, does that mean because you're going through
the data or you're gonna make more observations?
We cannot make any more observations, so it
really is about processing. It's really still trying
to figure out how our detector is inter
is collecting the data and what that means,
in terms of the exact wavelengths.
And, yeah, there's just a lot of data
there. We did some really cool different types
of studies of it. So we purposefully lined
up our slit, which is very, very narrow
slit, but it's long. It's seven and a
half degrees long by point one degree wide.
And we purposefully lined that up to be,
where the long part was kind of in
that sun, comet,
anti sun
tail direction so that we could capture that
tail. It turns out the tail was even
longer than we expected,
and the coma was even bigger than we
expected. But what we did was that so
because it was narrow, that means we're only
kinda getting a sliver of that sort of
region of space that's the the comet and
the tail and the anti tail.
But then we took the instrument,
well, we took the spacecraft, and and the
the NASA team did a fantastic job planning
this somewhat complicated
movement of the spacecraft
where they they moved our slit down off
the target and then all the way back
up over the target. And we did that
a couple of times. So we actually have
sort of different
time domain data. We have different,
different sort of views of different parts of
the sky with that data. And so, yeah,
there's still just a lot of data to
play with and try to interpret,
and then changes that we might be seeing
over the couple of hours that we were
pointing because I think we took observations over
about eight hours. So any kind of changes
in the emission rates of the gases,
would be a little bit more subtle, and
we have to kind of do the analysis
a little bit more carefully.
And while Europa Clipper isn't going to be
collecting more data, we do have actually really
cool data from the JUICE mission.
The JUICE mission is a European Space Agency
mission, and we have a sister
instrument, another UV instrument, onboard that mission called
Juice UVS.
And so that telescope is actually observing,
observed at the same time as the UV
data from Europa Clipper.
And more fast like, what's gonna be super
cool about that data, we don't have that
data yet. So there is still analysis to
be done.
That data, because of the geometry of where
Juice is right now, it can't send back
a lot of data just yet. So we're
expecting that data,
in the coming months to to come down,
and then we can analyze it. But what's
super cool about that is that
JUICE was kind of positioned closer to the
sun. So it's looking at the comet
from the perspective of the sun. So it's
gonna see sort of some of that reflected
light as well as the light that's,
still being emitted in that auroral fashion.
And then Europa Clipper was looking at it
almost completely from the night side. So they're
from two totally different angles we're gonna be
able to collect that data. And that's really
important because
things like dust, for example, if it's big
chunks of dust, reflect light. But when you
have, like, little tiny dust particles, they backscatter
light. So just like when you're kind of
in your kitchen or in your bedroom and
you get that beautiful, like, sunbeam in and
suddenly you realize, wow, my room's really dusty.
Like, there's dust floating around everywhere. That's because
those dust particles are backscattering light. You're not
ever standing in the sunbeam. You're looking at
the sun and the sunbeam, and that those
dust particles get highlighted in that way.
That's what Europa Clipper will be seeing, those
smallest particles from that perspective.
But Juice, looking at it from the other
perspective,
will see a different set of particle sizes,
because it's got this different observing geometry. So
that's one of the things that makes it
really cool is looking at one thing from
multiple angles gets us a lot more information.
And so we will be able to do
a even better analysis of the CLIPr data
when we can also see what happened with
the JUICE data.
You said there was carbon in it. Would
you expect to see that in comments? Yeah.
So from my understanding is that this object
in particular has actually
shown way more carbon.
It's had a higher carbon to water ratio
than any than most or all,
comets that have been observed from our own
solar system. And that
could be indicative of sort of what the
chemical makeup of the solar system that this
thing formed in is. Like, is it just
a more carbon rich solar system? Is that
the norm, or is ours the norm?
We don't know. And so we, we're not
surprised to see carbon in general,
but some of the observations have shown a
really high percentage of carbon to oxygen or
carbon to water.
And I don't think our data is showing
it to be quite that much, but we're
also a lot closer to the sun now.
So a lot of those observations started,
when the comet was still pretty far out.
It was out by the orbit of Jupiter.
And so
that's what's made this object so exciting is
that we've known about it for a long
time before we got to its, before it
got close to the sun, and we were
able to then see it start sublimating different
materials,
pretty early on in it on its pathway
towards the sun.
And even that part has been unique for
it. Like, the fact that it started sublimating
and being detectable
that far out might be a sign that
this object,
has never been close to a star before.
So this object could have been been formed
pretty far out from its host star and
launched out of the solar system before it
ever had a chance to get close to
it. And that might be why it started
sublimating so early as it came into our
solar system. And so it's a really unique
opportunity to see some of the, like, primitive
ices and volatiles that were on this object.
Basically, some of the the most natural formed
materials from its solar system as it comes
into ours. And so that's a very rare,
very cool opportunity for setting this object.
Do you know,
do people know do you know if if
because of the trajectory it's come from, whereabouts
in space it's coming? Not me personally. But,
yeah, there is an there there have been
studies on basically, its trajectory points to it
being from a a pretty old portion of
our galaxy.
And so it's probably been traveling for billions
and billions of years and probably came from
a solar system that that was forget the
exact age now, but much, much older than
our own solar system. And so that's
also very cool because
that could indicate, you know, the way that
we get a lot of the materials spread
through the solar system is through supernova that
kind of has some of that material. They
burn the material. They create the next level
up. Like, they burn the hydrogen and the
oxygen the hydrogen and
and, the helium, and then they can make
the higher, the heavier,
quote, unquote, elements like oxygen and carbons and
and everything else that we have all comes
from sort of you know, we're all made
out of stardust. Right? And so that those
materials are formed inside the star. So if
this is a more ancient solar system, it
may lack some of those,
the or at least lack the, the same
ratio or abundances
that we have in our solar system, which
is a more a younger, hipper
solar system, so to speak. And so understanding
those ratios even from just this one opportunity
to see this
semi pristine object,
is a really cool opportunity to understand how
other solar systems form and what's the genetic
makeup of those solar systems compared to ours.
So you say pristine, but it's it's traveled
a long way through space. Right? So that's
changed. That's a very good point. Yes. So
it is being exposed to constant, cosmic ray
radiation, and some of the observations have shown
that that probably
affects the outer parts of the,
of the comet itself as it's been traveling.
And so there is definitely some alteration. It's
not not oh, unfortunately, after billions of years,
nothing's very, very pristine anywhere.
But,
but, yeah, it hasn't been from what we
think, at least, it probably hasn't been heated
the to the level that most of the
comets that have kind of been on multiple
journeys around our sun have or, like, the
asteroids, for example, that are super overly heated.
And so you really do lose
some of those initial,
compositions that were kind of frozen in in
time,
and can stay frozen if they don't get
too too hot.
And so it's very fast moving. Does that
make it difficult to observe, or is it
does that not make a difference?
It does make a difference. Yeah. So it
depends on your spacecraft or your telescope.
The ones on Earth can track things pretty
easily, I think, because,
we have the mechanics to just keep, you
know,
track we just say track, and it and
it tracks.
Engineering's a wonderful thing.
But some for some spacecraft,
moving targets are hard to do. For example,
JWST
was designed to study astrophysical
objects. They're not supposed to move very fast.
But I think it's gotten some incredible data
of this target, so I don't think this
one was moving too fast for it. But
there are some,
objects, for example, that would be moving too
fast for Hubble or JWST or even for
Europa Clipper.
But we were able to,
to hold on to it perfectly. Again, the
the spacecraft team, the engineering team on Europa
Clipper was able to
set up this observation within two and a
half months
and figure out how to track it, and
everything worked really, really well. So our observations
are are beautiful.
Europa, right, completely full of waters. Do I
is it possible that that water came from
comets?
It's
possible that some of the water there
are
contributions from comets, but the the place where
Europa formed, it's actually
just an area where water
could be stable.
And so water is very abundant across our
solar system, and the reason we don't think
Earth's water is
sort of from the beginning is just that
we're much closer to the sun. And so
it should have all kind of heated off
at some point in the in the multiple
processes that the Earth underwent.
Certainly, some of those major impacts, including the
one that may have formed the moon. And
so we don't think we could have held
on to the sort of initial
inventory of water that would have been in
the solar system. But Europa is further out.
It's past what we call the snow line,
which is where,
liquid or solid water ice could kind of
still stay stable. And so Europa probably formed
with most of the water that it has.
And then, certainly, it's probably been bombarded by
other objects, asteroids that are water rich or
comets that may contribute and change,
its overall water
con like, water amount or,
style of water too because it can have
different sort of what we call d to
h ratio, the different kind of, levels of
hydrogen, types of hydrogen that make up the
h two o.
So, yeah, I mean, it it can be,
but most of it's water. It's it's a
natural comet in that sense.
I've spoken to,
scientists involved in in in sort of distant
space missions
over the years, and I don't think I've
ever spoken to somebody who's kind of,
you know, done this. Or they're on the
way somewhere, and then they've just thought, yeah,
we could look at that. So let's see
if we can. Is is it normal, this
kind of behavior?
It can be. So I think it's more
we don't usually get surprise visitors or that
we know about at least. So that part's
been really exciting.
There is often the opportunity to observe maybe
an asteroid that we're passing close to on
our way out. So there have been
observations of asteroids in the main belt, or
even near Earth asteroids as a spacecraft is
kind of on its main journey.
But, again, it makes such a good opportunity
to test out how all the instruments work
when you can observe something two years before
you get to your main target.
Once we get to Europa, it's gonna be
rapid fire. We're gonna be doing, 50 flybys
within three and a half years. And so
we're gonna be getting data, looking at the
data. As soon as we get the data,
we were gonna wanna figure out how we
wanna, you know, set up our detector for
the next observation. And it's gonna be so,
so fast that we're not gonna have
that much time to sit and
work and fully understand how the detector itself
is. You know, all of these detectors have
little quirks, and,
they're complicated. Right? You're they're not just your
cell phone camera. And even your cell phone
camera has a lot of calibration that goes
into it before it ends up in your
cell phone. And so you have to figure
it out. It's these are all custom designed
specifically for the missions that they're on. And
so,
yeah, we will it it's much better when
you can get one of these kinda surprise
or
or fortuitous
opportunities to observe on your way to the
target rather than waiting until you get there.
So it's been done before, but I don't
know of one where it's like, oh, surprise.
We just found found the object.
One, actually, one I'll take that back. So
one other example would be,
in some ways, is the New Horizons mission,
which I also work on. But, you know,
that one was destined to go to Pluto
and then to go and explore the Kuiper
Belt, but it wasn't guaranteed
that there would be an object for it
to do a second flyby of. Once it
got past Pluto, there wasn't a guarantee of
finding something else that it could look at.
And then, fortunately, through lots of,
observations and surveys of the Kuiper Belt, then
they were able to find,
Arrokoth, which ended up being the next flyby
target, for New Horizons. So that one may
be less of a surprise in that sense.
Like, they wanted to do that anyway, but
they had to look for it before they
could. Is it all solar powered? Have you
used some of the battery that you'd be
able to use elsewhere, or is it all
solar powered? Yeah. Europa Clipper has these huge
solar panels that are when when you fold
them all the way out, they're the size
of a basketball court.
So it's a massive spacecraft, massive solar panels.
That's where, most of the power is coming
from. We don't have anything
like, RTGs that have been on some of
the more deep space missions.
There's also some forms of propellant on there,
I think.
But,
the majority of the powering of the of
the spacecraft comes from the solar
power generated power. Right. So just quickly on
the horizon because it can't not.
Amazing images of Pluto that came from that.
That's kind of the thing that caught the
public attention particularly
after that sort of thing. Does that you
know, as a UV specialist, do you do
you want people to be more focused on
the UV?
I think any interest in a planetary body
is a good thing to have.
I do try to talk up the UV.
I think people don't think about the world
in the UV. Right? I mean, our eyes
see in the visible, so it makes sense
to want to see those visible color images.
But one of the powers of the UV
is that it is
seeing, you know, information that our eyes and
our regular visible cameras can't see, especially when
it comes to those kind of elemental
materials like I was saying in the in
the atmospheres.
One of the main ways we study in
the UV these bodies, not so much Pluto,
but Europa has an atmosphere. The comet is
obviously emitting light. It's it's those auroral emissions.
So you're actually seeing the aurora in many
ways with the UV
of of these different bodies. And so,
and the aurora that you see in the
UV is gonna be slightly different, than the
aurora that you would see in the visible.
And so it could tell you either you
can kinda get,
you know, oxygen has a rural emissions in
both UV and in oxygen, but you can
understand more about
how much oxygen must be there if you're
depending on the ratio you see in the
UV versus the visible. But then there are
other materials that won't have a rural emissions
in the visible that do in the UV
and vice versa. And so you kind of
want to look at everything,
from as many different eyes and eye styles
as you can to get the full picture
of what's going on with any object in
the solar system. So we don't see the
UV, but there are,
creatures on Earth that do. Right?
Yeah. I think bees
and probably some other ones,
but these are the ones that I know.
But it's cool. Yeah. Because and I don't
know the extent of what bees can see.
Like, do they see the UV and all
of the colors that we see, or does,
like, their eyes cut off at,
green? I I don't know.
But it could be. And so, yeah, and
some animals can see into the infrared, which
is also a really powerful part of the
of of the spectrum for understanding, like, mineralogy
of of rocks and and materials. Because it's
it's tempting to think of the visual from
our perspective as being the world as it
is, but, you know, there are literally things
flying around us that that see the UV
that you're studying. It's brilliant.
Yeah. And it makes sense for humans' eyes
to be focused on the visible because the
UV is very hard.
We don't get a lot of UV light
through our atmosphere. Our atmosphere
absorbs most of the sunlight that's coming in
the UV. The stuff that does get through,
of course, burns our skin and things like
that, so we have to be careful.
But we can't do UV observations from Earth
based telescopes, which is also why you don't
hear about,
UV data as often, I think, because the
only way to collect UV data is from
space. You have to be up above the
atmosphere.
And so,
assets like the Hubble Space Telescope
observing the UV and then all of these
spacecraft observing the UV, but you can't go
to, like, a a nice telescope at the
top of a mountain
and get UV data. It's harder to get.
It's rarer to get, but it's still extremely
powerful. We'll hear more from Michelle later in
the podcast. But I wanted to know more
about this fascinating mission,
comet interceptor, one of the most audacious wait
and see projects in the history of space
exploration.
With the famous Rosetta mission to 67 p,
we had years,
even decades to study the target from afar.
We know the orbit, the size.
But the thing with those comets is that
they are short period comets. They've been around
the sun many times, and therefore,
they're weathered,
heat blasted, and altered. And that's why scientists
really want the sort of comet that they'd
be able to catch with comet interceptor.
If a comet that had spent a long
time in deep freeze in space,
perhaps somewhere in the Oort Cloud got nudged
out and towards us,
then lying in wait
will be comet
interceptor.
Now in this conversation, you'll hear the term
Lagrange points. They're named after the mathematician, Joseph
Louis Lagrange,
and they are gravitational
sweet spots in space where something like a
small satellite or indeed the comet interceptor project
spacecraft can stay in a fixed position
relative to the Earth and the sun, enabling
the spacecraft
to effectively hover in space using very little
fuel. Here's ESA scientist, Michel Kuepes. I'm working
on the comet interceptor mission,
which is
an ESA mission incorporation
with JAXA, the Japanese
aerospace agency,
and it's currently being built.
Launch is foreseen in late twenty eight or
early twenty nine,
and
Comet
interceptor will be parked in the L two
Lagrange point
behind the Earth as seen from the sun,
roughly a million and a half kilometers behind
the Earth as seen from the sun, and
they'll wait on its target.
And,
essentially, then where,
when it's time to to to leave to
to encounter the target, leave L two and
be transferred to the target, which it will
meet most likely at the point where the
target comet causes a eclipse. Okay. What l
s l s s Oh, sorry. LSST is
a legacy
survey in space and time,
and it's essentially the the Vera Rubens telescope,
a new eight meter survey telescope
that's currently
starting to operate
in in Chile,
and it will
image
the sky visible from roughly
once every three days.
And the last I heard is actually that
the survey will
that the survey will start mid mid this
month.
I'll get an update actually today or tomorrow
on that, but the survey is now going
to to start very soon. Now the sparking
is done because for those comets are typically
detected only a couple of months or a
year before they
before they before they perihelion. Now
comet interceptor relies that with LSST, this
time increases to several years, but even several
years is not enough to def to to
to define,
design, build,
and fly a space mission. Therefore, comet interceptor
is being built now and waits
in l two. And then with a typical
transfer time of one or two years,
it's feasible to fly by a reachable comet
if it's detected
on time by by LSSD.
You've got your spacecraft parked at Lagrange 0.2.
There's a comet coming.
If it was
three I Atlas,
would you have been able to use interceptor
on that?
No. It's,
it's it's would not have been reachable with
a fuel available on Comet Interceptor,
and it's still a little bit far out.
So the Comet Interceptor
spacecraft
is able to to encounter
targets, well, which can be reached with the
fuel and also has to be relatively close
to Earth's orbit, ideally between point nine and
one point two AU.
There is maybe a little bit of margin
of it,
but, see, I was already too far out
from that.
And the other aspect
is
comet interceptor
is designed
against flyby velocities of up to 70 kilometers
per second.
And ATLAS,
I don't know what's the hypothetical
velocity. Flyby velocity would have been as kind
of worst case in terms of
flyby velocity
as an
interstellar object with a very high eccentricity
and
on a nearly retrograde orbit. So most likely,
also, the flyby velocity would have been too
high.
Okay. But it so you're looking at comets
which are,
within our solar system,
born in our solar system. So Yes. And,
so have you got particular targets that you're
looking at? No. We do not. I mean,
the target still has to be detected.
In the
unlikely case
that
no comet will be found that can be
encountered in the up to six years in
space for comet interceptor,
We have a list of short period comets
as backup targets.
So for for
for each launch,
yeah, we we we have,
depending on the exact launch date, we have
two or three backup targets
that could be reached in case we do
not find a a long period, Comet.
Okay. Fair enough. And so when, when you
do get your target, you fly your spacecraft
to it.
What happens then?
Okay.
So comet interceptor,
actually, three spacecraft.
So the main comet interceptor spacecraft and two
small spacecraft that we call probes b one
and b two,
with probe b one contributed
by YAXA
and probe b two by ESA.
And one one to two days before the
flyby, the probes will separate
and approach the nucleus a bit closer than
the main spacecraft.
And then
the actual science mission out as a prime
science mission is is is essentially only a
few minutes when the spacecraft are close to
the close to the comet.
And space the main spacecraft will fly by
at a nominal distance of 1,000
kilometers, which may be a little bit modified
based on comet activity.
And based on the flyby velocity, it may
get a bit closer.
And we'll essentially
collect all the data. It can
in the time of the closest approach and
afterwards use up to half a year for
the downlink of the data.
The small sats will go closer with a
nominal distance
of,
400 kilometers for one of them and around
800 for the other.
We'll do the same. We'll take all the
data they can in the hours before closest
approach and during closest approach and send the
data back to the main spacecraft through an
inter satellite link.
And then everything will be downloaded from the
main spacecraft
to Earth. What does the having the three
different spacecraft bring?
One thing is,
that we get multipoint observations.
So we sample different
areas of the coma at the same time
with the three spacecraft, and we also get
some stereo view on the nucleus.
And the other aspect is with the small
satellites,
we are willing to take a little bit
more of a risk
and to get closer to the nucleus of
the comet. Bit more disposable.
Yeah. More disposable in a sense. Yeah.
Imagine that you could
use,
interceptor to look at three I Atlas.
What,
what would it what
extra information would it give us? Yes. One
thing is we would get high resolution. High
resolution, meaning a couple a couple of meters
per pixel
images of the nucleus.
We would also get a much more detailed
coma composition
mainly because comet interceptor is flying a mass
spectrometer
that's similar to receptor.
So to reset
up, can get many observations at the same
time.
Many molecules at the same time. Sorry.
And
we get some some the soft also infrared
spectra that show
the the variation of composition over the surface
that shows the thermal properties, some, yeah, some
physical properties of the surface.
And,
we we get a lot of information
also about the the plasma environment
and the and the outer commas who the
who the spacecraft
observing at at the same time between the
case of an interstellar object may not be
the highest priority.
Just talking about this, there's there's there's there's
there's been three interstellar objects.
I presumably, there have been
many more interstellar objects. And the reason we've
seen three is because we now have the
instrumentation, whatever it is, to to be able
to detect Indeed. There are many more of
them, and
we only detect,
let's say, the brighter ones and the ones
that come in close.
And, yeah, as I already indicate,
also, the reason that all three have been
detected
in the last ten years is simply because
of more
of more advanced
instrumentation.
And with LSST,
we get we hope to get get more.
Maybe, I don't know,
maybe 10 or 100 more. It's really very
difficult to predict on the small statistics and
objects we are having. Yeah. Yeah. I mean,
I was gonna ask you a silly question.
But, like, do you do you think that
Oumuamua, for example,
is is actually common,
relatively common, or do you think that was
really a a one off? I mean, we
don't know right now. Is that what? Sorry.
Oumuamua. Yeah.
Was it I don't know. No. I mean,
with with I mean, it was its properties
were unexpected.
And, of course, based on the discovery of
one object
and the total of three, it's very hard
to say if it's. So
so my guess is as good as yours.
It's it sounds like to me
that this is going to become,
the it's it's a very exciting area of
science. If you're interested in in space, which
I certainly am, then this is a very
interesting area of science. You know? Interstellar,
objects coming through our solar system, comets within
our solar system, flying spacecraft to comets within
our solar system. It sounds like it's an
area of science which is
developing more and more. If we've only found
three so far, it's a bit like exoplanets.
Right? There was a time when we thought
they were going to be exoplanets, and now
there's thousands and thousands that we know of.
Yeah. In a sense, it's maybe like exoplanets
since the nineteen nineties.
Obviously,
ESA had the Rosetta mission that go into
a comet ten years ago.
Why do we need comet interceptor as well
on top of that? The other thing is
we had comet 67 p, which is a
small period comet that orbits the sun every
six years.
And did and and and
and, yeah, observed it and its evolution in
very much detail. But the interesting thing is
for some of the large structures like the
the supposed layers,
the two
there's a two bodies, the the kind of
by contact binary structures, the big,
the the big holes that we have seen.
There are still a discussion ongoing
for many of those things to which extent
they are primordial.
They are remnants of the formation and to
which extent
they have been created
by the many orbits around the sun and
the many warming up,
periods
in the sun.
And they are a mission that gets at
least those large structures also on a on
a
on a new comet that comes into the
inner solar system for the very first time
will help to distinguish
which of those structures have been,
yeah, are there as well. And if they're
on the new comet as well, they are
indeed primordial.
If they are not there,
they may be
they may be a consequence
of the of the evolution due to the
formations for the inner solar system of a
comet like 67
b. So in those sense, those missions are
complementary, and comet interceptor may also help with
an with the analysis or reanalysis
of the of the of the results from
Rosetta.
Now I did mention at the start of
this podcast, and you'll no doubt be aware,
there is speculation in the press that maybe
three I Atlas is some sort of alien
spacecraft or something to do with alien technology,
which has been sent to
our solar system. Now we don't want to
get into conspiracy theories here on the Physics
World Stories podcast. Of course, we're far more
interested in the universe as it actually is.
But from a science communication point of view,
it's something that I wanted to talk to
Tracy Becker about. Because doctor Tracy Becker was
the winner of the Carl Sagan Award for
the Public Appreciation of Science in 2023.
And I wondered what her take was on
this story of fascinating story of an interstellar
comet being mixed up in the media, in
some cases inspired by comments from scientists who,
for whatever reason, seem to say that anything
that is slightly peculiar
might well be alien technology.
My feelings can be mixed. I mean, I
think that anything that gets people excited and
talking about space and focused on space and
understanding that there's all these really cool phenomena
happening all the time around us and and
focusing on the science,
that's all exciting. So I'm, in some ways,
glad to have so much interest generated in
this object. We don't get a lot of
interest generally just from a an average comet
passing by.
This object, of course, is spectacular in the
sense that it's only the third time we've
ever known about an interstellar visitor. Right? This
is an object that came from outside of
our solar system, and it's in our solar
system. And so it rightfully deserves
a lot of talk and a lot of
press. And so from that perspective, it's good
to see,
so much interest in it. What I hope
that the public does is
take that initial, you know, a little bit
of bait, I guess, in terms of
of what is this thing
and and then go look at it more
carefully and see, wow. This is really cool
even though
the bait was this kind of alien thing
that people like to throw out there.
But the the actual science behind it is
interesting. The part that I waiver on a
little bit is that, you know,
the public we want the public to trust
scientists.
There's already a lot of, erosion of trust
in scientists
and science in general
in multiple fields. And so
experts kind of throw out claims that are
not
backed
by empirical evidence,
can further tarnish and further hurt sort of
that goal of making sure we're communicating,
good science and making sure that that people
understand the science and trust the science and
trust the scientists.
I hope that people use it as a
launching point of saying, what? Aliens? Oh, no.
That's it's not aliens, but this is cool.
And not the other way, which could be,
oh, it's aliens.
Oh, wait. No. All these other scientists are
saying no. I guess science never can con
can come to a conclusion on anything, and
now I don't believe any of it. You
know? That's a harmful,
response to it. So,
yeah, I think a mix.
But, hopefully, again, people just appreciate how how
cool this is. And I think the images
that,
Hubble and other telescopes have been producing
and the results that hopefully we'll be publishing
with Europa UBS and other spacecraft
will keep that interest alive,
and just show how cool it is to
be able to have this fleet of spacecraft
all be able to turn and point at
this one really
special,
interstellar object that serendipitously came through our solar
system at the right time. Stay tuned for
whatever for the results that we do publish
with this instrument and with the various other
spacecraft and,
telescope ground based telescope observations that are happening
because I think we're just scratching the surface.
We just kind of are taking images right
now and and getting some of that initial
data out there, but this is our first
real opportunity to understand
and kind of put into
context what our solar system is. You know?
When we look at we can look at
planets now.
We can see these exoplanets around other stars,
which is fantastic.
But it's hard to get any compositional information
about those, and and even then, it's some
of the usually the biggest ones.
It's hard to get information about comets in
our own solar system that don't come close
to the Earth,
or come close to the sun, let alone
comets from other solar systems. So this is
really one of those extremely rare opportunities
to potentially understand sort of that reservoir of
materials that form
the
the basic building blocks of another solar system
and ask those questions. You know? How unique
is our solar system, or how common is
it? And are we the weird ones? Is
that solar system the weird one? We won't
know that until we start getting more and
more of these objects. And I think what's
really exciting is that we do have these
powerful telescopes like Vera Rubin and others coming
online where we're gonna be able to see
and detect some of these objects way earlier
out. You know, this is the third one
we've known about, but it's certainly not the
third one that's ever come through our solar
system.
But having the opportunity to detect them in
advance
and seeing the results of and the the
power of having gotten these observations and working
together across all these missions,
and across the ground based telescope network to
study it,
I think that we're gonna see this more
and more and more, and that's something exciting.
We're on the precipice of understanding
other solar systems in a way that we
weren't really expecting to do. Right? We're trying
to understand you know, build a bigger telescope
so that we can,
see further further and further out. But this
is an opportunity to make sure we're also
ready
to see the things that come come into
our backyard and actually get to play with
a little bit.
I'd like to thank Tracy and Michelle for
talking to me for this episode of the
Physics World Stories podcast. Don't forget that physicsworld.com
is an excellent resource for everything
to sate your desire for the latest
and greatest
of astronomy and space news. I hope 2026
has been treating you well so far, and
we'll be back next month with something else
from this wonderful world of physics. And thank
you very much for listening.